Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) $ in Millions		12 Months Ended
		Dec. 31, 2016 USD ($) equipment	Dec. 31, 2015 USD ($)
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	$ 30,118	$ 27,603
Accumulated depreciation and amortization	[1]	10,961	10,347
Property and plant, before construction work in progress	[1]	19,157	17,256
Property, Plant and Equipment, Net	[1]	$ 20,113	18,799
Number of combustion turbine electric generation equipment under capital lease agreements | equipment		2
Number of capital lease agreements | equipment		2
Capital lease agreements, gross asset value		$ 232	233
Total accumulated depreciation, capital lease agreements		77	72
Held-to-maturity Securities		282	288
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	10,911	10,431
Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	10,850	10,255
Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	3,879	2,774
Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	2,641	2,442
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2],[3]	1,837	1,701
Construction work in progress	[1]	750	1,268
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	[1]	206	275
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	18,959	17,966
Accumulated depreciation and amortization	[1]	7,880	7,460
Property and plant, before construction work in progress	[1]	11,079	10,506
Property, Plant and Equipment, Net	[1]	11,478	11,183
Union Electric Company | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	10,911	10,431
Union Electric Company | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	5,563	5,303
Union Electric Company | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	1,151	979
Union Electric Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2]	455	445
Union Electric Company | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1],[2],[3]	879	808
Construction work in progress	[1]	193	402
Union Electric Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	[1]	206	275
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	10,208	9,250
Accumulated depreciation and amortization		2,850	2,632
Property and plant, before construction work in progress		7,358	6,618
Property, Plant and Equipment, Net		7,469	6,848
Ameren Illinois Company | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	0	0
Ameren Illinois Company | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	5,287	4,952
Ameren Illinois Company | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	2,016	1,674
Ameren Illinois Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	2,186	1,997
Ameren Illinois Company | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2],[3]	719	627
Construction work in progress		111	230
Ameren Illinois Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress		0	0
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	951	387
Accumulated depreciation and amortization		231	255
Property and plant, before construction work in progress		720	132
Property, Plant and Equipment, Net		1,166	768
Other | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	0	0
Other | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	0	0
Other | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	712	121
Other | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2]	0	0
Other | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[2],[3]	239	266
Construction work in progress		446	636
Other | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 0	$ 0
Minimum | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		5 years
Minimum | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		18 years
Minimum | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		50 years
Minimum | Gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		20 years
Minimum | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		5 years
Maximum | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		100 years
Maximum | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		75 years
Maximum | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		75 years
Maximum | Gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		80 years
Maximum | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		55 years
Maximum | Union Electric Company | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		150 years

[1] (a)Amounts in Ameren and Ameren Missouri include two CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $232 million and $233 million at December 31, 2016 and 2015, respectively. The total accumulated depreciation associated with the two CTs was $77 million and $72 million at December 31, 2016 and 2015, respectively. In addition, Ameren Missouri has investments in debt securities, classified as held-to-maturity and recorded in "Other assets" that are related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2016 and 2015, the carrying value of these debt securities was $282 million and $288 million, respectively.

[2] (b)The estimated lives for each asset group are as follows: 5 to 100 years for electric generation, excluding Ameren Missouri's hydro generating assets which have useful lives of up to 150 years, 18 to 75 years for electric distribution, 50 to 75 years for electric transmission, 20 to 80 years for natural gas, and 5 to 55 years for other.

[3] (c)Other property, plant, and equipment includes assets used to support multiple utility services.